Everything You Must Know About Iterator In Java

Table of Contents [show]

Introduction

A Java iterator is an object to iterate through elements or arguments in a collection. It comes from the technical word "iterating," which refers to looping through. An iterator is used in Java to go through any collection of objects. To use the iterator, import the java.util package and apply the iterator() method. The iterator can then carry out various actions on the collection. An iterator method in java is one of the ways to traverse a collection. It was introduced in Java 1.2 as a replacement for Enumerations.

Iterator in Java introduced improved method names and made it possible to remove elements from a collection. However, it doesn't guarantee iteration order. Read on to know more about Java Integrator.

What Is The Use Of An Iterator In Java?

A user must create an instance of the Iterator interface from the collection of objects they wish to travel across to use the Java Iterator. Following that, the receiving Iterator keeps track of each component in the underlying collection to ensure that the user will iterate through every object in the collection.

The user may update the underlying collection when traversing over an Iterator leading to that collection. Then the Iterator will identify it and will throw an exception the next time when the user tries to get another component from the Iterator.

Our Learners Also Read: What Are Java Classes and Objects and How Do You Implement Them?

What Are The Java Iterator Methods?

The Java Iterator contains a total of four methods that are:

1. boolean hasNext()

This method simply denies and does not accept any parameter. When there are more elements left in the iteration, it will return a true value. However, if no more elements are left, it will return false. Also, if there are no more elements left in the iteration, calling the next() method is not needed. Hence, this method determines whether to call the next() method or not.

2. E next()

It is the same as the hasNext() method. It will not accept any parameter. It returns E which is the next traversal element. If no more elements are left to iterate in the collection of objects then it throws the 'NoSuchElementException'.

3. default void remove()

This method will not need any parameters. Also, it has no return type. Removing the last element returned by the iterator traversing through the underlying collection is the main function of this method. Although, the remove () method can be requested only once per the next () method call. When the remove operation is not supported by the iterator, then it throws the 'UnSupportedOperationException'. It will even throw the 'IllegalStateException' when the next method is not called.

4. default void forEachRemaining(Consumer action)

The only method of Java Iterator which accepts a parameter. It takes action that has to be performed, as a parameter. This method has no return type. It performs the particular operation on all of the left components of the collection. It continues until all the components are consumed or the action throws an exception. These exceptions are thrown by action delivered to the caller. When there is a null action, it will throw a 'NullPointerException'.

Quick Facts About Java Iterator

• It is an interface added to the Java Programming language. It is added in the Java 1.2 Collection framework and lies in java.util package.
• The Java Iterator can one by one iterate the components of the collection object.
• It is a Java Cursor that can traverse the objects of the collection framework.
• The methods names of the Java Iterator class are very simple and easy to use.
• The Java Iterator is also called the Universal cursor of Java. Since it is suitable for all the classes of the Collection framework.
• The Java Iterator can support the READ and REMOVE operations.

Iterator Java Example

Let us understand Java iterators with the help of the following example:

// Import the ArrayList class and the Iterator class

import java.util.ArrayList;

import java.util.Iterator;

public class Main {

  public static void main(String[] args) {

    // Make a collection

    ArrayList cars = new ArrayList();

    fruits.add("Mango");

    fruits.add("Banana");

    fruits.add("Apple");

    fruits.add("Cherry");

    // Get the iterator

    Iterator it = fruits.iterator();

    // Print the first item

    System.out.println(it.next());

  }

}

What Is The Syntax Of An Iterator In Java?

The syntax of iterators in java is simple and easy to remember.

Iterator itr = c.iterator();

Where 

c is a Collection object. 

itr is an Iterator interface type referring to c

Advantages Of Iterator In Java

Iterators simplify the code to make it general and easy. The Iterator allows modification of a collection while traversing it. It is hard to do with a simple for or while statement. The iterator loops through the objects of a collection. It reads them and removes them. 

Since the iterator interface is universal, you can apply it to any collection object. The Java iterator is also a universal cursor for collection API. It has the additional function of removing elements from collections. 

Points To Remember About Java Iterators

• You can apply them to any of the classes of the Collection framework.
• In Java Iterator, both the read and remove operations work.
• If a user is working with a for loop, they cannot modernize i.e. add or remove the Collection. However, in the case of Java Iterator, they can easily update the Collection.
• The Java Iterator has also been termed the Universal Cursor for the Collection API.
• The method names in the Java Iterator are very easy to use.

One can gain more knowledge about Java iterators through java online courses.  Since Java is popular for its versatility and ability to create various applications, learning Java opens up many possibilities. Once you learn Java, you can develop large systems, software, and mobile applications. You can learn Java coding fundamentals and practice your skills with real-world projects.

What Are The Boundaries Of Iterator In Java

Although Java Iterators can perform many operations in a collection, there are some limitations to it. A few limitations of iterators in Java include:

• No support for backward-direction iteration
• It does not allow adding new elements to the collection
• No support for updating operations on the collection
• Java Iterator does not approve the replacement and extension of a new component.
• Java Iterator does not hold the various operations like CREATE and UPDATE in the CRUD operations.
• In parallel pattern, Java Iterator does not support traversing elements. Java Iterator supports only Sequential iteration.
• It also does not support more reliable execution to traverse the bulk volume of data.

Conclusion

A Java iterator can address the limitations of enumeration. It is crucial for any iteration programmer. There are a few limitations to these irritations but that does not degrade their importance. The syntax for Java Iterator is easy. Even beginners can understand the simple examples and apply them to their project.Java iterator methods are easy to understand and execute. You can gain better insight by joining a Java Full-Stack Developer Course. 

Get Started With A Full-Stack Java Developer Course

If you are interested to learn more about the fundamentals of Java, then enroll in a Full-Stack Java Developer Course. Check out E & ICT Academy IIT Guwahati in Full-stack Java Development which is designed for students and working professionals. You will get training with top trainers along with hands-on experience. 

About The Author: